I need some tips (problems once I transport to TotLM)

[Klorox]

The problem is that all the monsters really give me a hard time!

They seem to target my weaker party members and I can't get my good spells off (like Call Lightning and Static Charge).

Any and all tips are appreciated here!

[Crenshinibon]

This may not have been the best way to deal with them, but I finished TotL with a fighter/mage/thief and a bard, finding it nearly impossible to complete without spell buffs. The weaker characters you talk about, I assume they're spell casters, so you should probably make a monster wall or keep them a good distance away from combat, perhaps using the fling spell and run technique. If you have a strict healer character, sanctuary is perfect, as defensive and buff spells don't break it.

Tensor's, Blur, Mirror Image and Haste were my favorites. The Girdle of Ogre blood is a good item to provide five summons to take the enemies' attention off your party. Don't forget to haste your summons. It significantly increases their damage output.

If you have any thieves, the hit and run for backstab works wonders as well.

[Aerich]

Protect yourself from harpy songs and the like. In the courtyard, get yourself into a protective formation ASAP. Don't forget to have your best tank a couple of steps forward to act as primary target. Use spells to stun/enchant non-undead monsters. Holy Word has a spellcasting time of 1, and Chaos sets the harpies to fighting each other.

The Crypt shouldn't be too bad if you can keep most of your group together - use Turn Undead for some (hopefully) easy kills.

Spectral Guards are tough. Get yourself into a doorway and block it, either with a tough summons or a slashing-immune character. Then go to town with spells and missiles. Send a tank (preferably with speed boots and/or a potion of invisibility) to draw attention from more guards, and be very careful about straying from the doorway.